228

CONDENSERS AND COOLING TOWERS

across the tubes is kept more nearly constant than it is, for instance, in a
condenser of rectangular cross-section, and thus stagnation among the tubes
is largely obviated. The air and water of condensation are extracted at
different points, and a few of the bottom tubes are allowed to flood, so as to
cool the water somewhat before passing to the pump. This makes the
water-extraction pump more certain in action, but in general it is hardly
desirable to cool the water of condensation when it is to be pumped back
into the boiler, because of the loss of heat entailed by cooling the feed un-
necessarily. When the condenser is designed for high vacua in connection
with steam turbines, flooding of the lower tubes would be dispensed with,
and a baffle introduced to cut off some of the tubes for devaporizing the air
on its way to the air-pump suction. It is seen from the longitudinal section
in fig. 10 that the water is here arranged to make four passes from the inlet
to the outlet. This arrangement may be modified, of course, according to

circumstances, but, all other things equal,
the greater the number of passes the shorter
is the condenser and the greater is the
number of tubes. A condenser of this shape
does not need to be placed in the vertical
position. To save head room it can easily
be arranged with one of the inclined sides
on the foundations, the condenser then lying
on its side.

In regard to the best diameter of tubes
to be employed, this depends to a large ex-
tent on the conditions of the water-supply.
The smaller the diameter of the tube the

more effective is the surface from a heat transmission point of view, but
few makers care to insert tubes less than f in. outside diameter (thick-
ness No. 18 W.G., or 0-049 in-)> even when the circulating water is quite
clean. Three-quarters of an inch is the standard used by most manu-
facturers, but where the water is more or less dirty, and therefore liable to
choke the tubes, it may be necessary to adopt tubes of i in. diameter.

The usual arrangement of packing, and the gland ferrule for the ends of
the tubes, is shown in fig. n. The tube-plate is bored slightly larger than
the diameter of the tube, and is also screwed to accommodate the ferrule.
To make the gland water-tight, soft yarn treated with linseed-oil or tallow is
inserted, and the ferrule screwed down on it. It is advisable to have the
inside edge of the ferrule rounded off, as shown, to reduce the loss of energy
of flow at the inlet to or outlet from the tubes. Until recently it was the
common practice to bolt the tube-plates to the ends of the condenser shell,
and with the end covers bolted up against the tube-plates, as is shown in
fig. 6, p. 224. There is thus a made joint between each tube-plate and the
shell which it is impossible to re-make without detaching the tube-plate and
the tubes. A more modern arrangement is that shown in fig. n, where the
joint subject to the vacuum is between the cover and the shell, and can be

Fig. ii.—Attachment of Condenser Tube
and Tube-plate